Ground fog, also known as radiation fog, forms when air is cooled to its dewpoint temperature and becomes saturated. It
is a common occurrence on clear summer mornings when winds are light,
which favors full radiational cooling. In these situations, the
atmosphere cools off closest to the ground which may result in very
shallow fog, sometimes only a few feet deep. In this case, the fog
formed over a field of crops, which added extra moisture to the air
through transpiration.